Field of the Invention
The present invention relates to a novel delayed fluorescence material and to an organic electroluminescence material using the delayed fluorescence material.
Description of the Related Art
Studies for increasing the light emission efficiency of organic electroluminescent devices (organic EL devices) are being made actively. In particular, various studies of developing novel light-emitting materials for attaining more efficient light emission are being made. Among them, a delayed fluorescence material for delayed light emission is expected as a material that has a latent possibility of drastically increasing light emission efficiency. Until now, some delayed fluorescence materials containing a metal of Cu, Pt, In, Pd, Sn, Zn or the like have been proposed (for example, see Patent References 1 to 3).
On the other hand, only a few studies have heretofore been reported relating to a delayed fluorescence material that comprises an exciplex prepared by combining an acceptor compound and a donor compound. Non-Patent Reference 1 says that an external quantum efficiency of 3.4% could be attained by the use of an exciplex composed of N,N′-diphenyl-N,N′-(2-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) and 2,5-di(3-biphenyl)-1,1′-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP). On the other hand, Patent References 4 and 5 say that forming an exciplex reduces light emission efficiency.